Transition metal catalysis remains a key enabling technology for the production of fuel. The petroleum upgrading process, particularly hydrotreatment, involves the reductive cleavage of polar bonds such as carbon-sulfur and carbon-nitrogen bonds, processes commonly referred to as hydrodesulfurization (HDS) and hydrodenitrogenation (HDN), respectively. The efficient and complete removal of sulfur and nitrogen atoms is desired for the production of environmentally safe fuel because the combustion of sulfur- and nitrogen-containing components of petroleum results in increased emission of gaseous pollutants (SOx and NOx) to the atmosphere.
Current hydrotreatment catalyst technologies are energy intensive (R. R. Chianelli et al. Catalysis Today 147 (2009) 275-286). This is due in part to the reaction conditions required for the metal catalysts to function. For example, cobalt- and nickel-promoted catalysts, such as CoMoS2 and NiWS2, generally function at high temperatures and high hydrogen pressures. These heterogeneous catalysts, in some cases, function at temperatures ranging from 300-650° C. and hydrogen pressures ranging from 90 to 120 atm or higher. The range of process conditions varies with catalyst formulation. These high temperature and high pressure conditions add to the refining costs of petroleum and crude oil. Hence, there remains a demand for cost-effective catalyst technologies for petroleum upgrading.
Industrial HDS and HDN catalysts generally comprise second- and third-row transition metals such as molybdenum, tungsten and platinum, usually in combination with ruthenium, cobalt or nickel promoters. The utilization of these relatively expensive and rare transition metals further raise barriers for the sustainability of industrial hydrotreatment. Hence, it is desirable to obtain high activity catalysts for HDS and HDN from inexpensive and terrestrially abundant first-row transition metals.
First-row transition metal catalysts have traditionally been believed to possess intrinsically low activity. However, results of studies on commercial CoMoS2 catalysts can be interpreted to suggest that the active sites of the catalysts may be the cobalt rather than the molybdenum centers. Examples of these studies are detailed in papers such as (1) Duchet, J. C.; van Oers, E. M.; de Beer, V. H. J.; Prins, R. J. Catal. 1983, 80, 386; (2) Vissers, J. P. R.; de Beer, V. H. J.; Prins, R. J. Chem. Soc. Farady Trans. I. 1987, 83, 2145. These results suggest that catalysts containing transition metals such as cobalt may be useful in catalysis. In particular, late first-row transition metals such as Fe, Co and Ni are relatively inexpensive and abundant, making them good candidates for use in HDS and HDN.